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package java.security.cert;

import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidParameterException;
import java.util.Set;

/**
 * Parameters used as input for the PKIX {@code CertPathBuilder}
 * algorithm.
 * <p>
 * A PKIX {@code CertPathBuilder} uses these parameters to {@link
 * CertPathBuilder#build build} a {@code CertPath} which has been
 * validated according to the PKIX certification path validation algorithm.
 *
 * <p>To instantiate a {@code PKIXBuilderParameters} object, an
 * application must specify one or more <i>most-trusted CAs</i> as defined by
 * the PKIX certification path validation algorithm. The most-trusted CA
 * can be specified using one of two constructors. An application
 * can call {@link #PKIXBuilderParameters(Set, CertSelector)
 * PKIXBuilderParameters(Set, CertSelector)}, specifying a
 * {@code Set} of {@code TrustAnchor} objects, each of which
 * identifies a most-trusted CA. Alternatively, an application can call
 * {@link #PKIXBuilderParameters(KeyStore, CertSelector)
 * PKIXBuilderParameters(KeyStore, CertSelector)}, specifying a
 * {@code KeyStore} instance containing trusted certificate entries, each
 * of which will be considered as a most-trusted CA.
 *
 * <p>In addition, an application must specify constraints on the target
 * certificate that the {@code CertPathBuilder} will attempt
 * to build a path to. The constraints are specified as a
 * {@code CertSelector} object. These constraints should provide the
 * {@code CertPathBuilder} with enough search criteria to find the target
 * certificate. Minimal criteria for an {@code X509Certificate} usually
 * include the subject name and/or one or more subject alternative names.
 * If enough criteria is not specified, the {@code CertPathBuilder}
 * may throw a {@code CertPathBuilderException}.
 * <p>
 * <b>Concurrent Access</b>
 * <p>
 * Unless otherwise specified, the methods defined in this class are not
 * thread-safe. Multiple threads that need to access a single
 * object concurrently should synchronize amongst themselves and
 * provide the necessary locking. Multiple threads each manipulating
 * separate objects need not synchronize.
 *
 * @author Sean Mullan
 * @see CertPathBuilder
 * @since 1.4
 */
public class PKIXBuilderParameters extends PKIXParameters {

  private int maxPathLength = 5;

  /**
   * Creates an instance of {@code PKIXBuilderParameters} with
   * the specified {@code Set} of most-trusted CAs.
   * Each element of the set is a {@link TrustAnchor TrustAnchor}.
   *
   * <p>Note that the {@code Set} is copied to protect against
   * subsequent modifications.
   *
   * @param trustAnchors a {@code Set} of {@code TrustAnchor}s
   * @param targetConstraints a {@code CertSelector} specifying the constraints on the target
   * certificate
   * @throws InvalidAlgorithmParameterException if {@code trustAnchors} is empty {@code
   * (trustAnchors.isEmpty() == true)}
   * @throws NullPointerException if {@code trustAnchors} is {@code null}
   * @throws ClassCastException if any of the elements of {@code trustAnchors} are not of type
   * {@code java.security.cert.TrustAnchor}
   */
  public PKIXBuilderParameters(Set<TrustAnchor> trustAnchors, CertSelector
      targetConstraints) throws InvalidAlgorithmParameterException {
    super(trustAnchors);
    setTargetCertConstraints(targetConstraints);
  }

  /**
   * Creates an instance of {@code PKIXBuilderParameters} that
   * populates the set of most-trusted CAs from the trusted
   * certificate entries contained in the specified {@code KeyStore}.
   * Only keystore entries that contain trusted {@code X509Certificate}s
   * are considered; all other certificate types are ignored.
   *
   * @param keystore a {@code KeyStore} from which the set of most-trusted CAs will be populated
   * @param targetConstraints a {@code CertSelector} specifying the constraints on the target
   * certificate
   * @throws KeyStoreException if {@code keystore} has not been initialized
   * @throws InvalidAlgorithmParameterException if {@code keystore} does not contain at least one
   * trusted certificate entry
   * @throws NullPointerException if {@code keystore} is {@code null}
   */
  public PKIXBuilderParameters(KeyStore keystore,
      CertSelector targetConstraints)
      throws KeyStoreException, InvalidAlgorithmParameterException {
    super(keystore);
    setTargetCertConstraints(targetConstraints);
  }

  /**
   * Sets the value of the maximum number of non-self-issued intermediate
   * certificates that may exist in a certification path. A certificate
   * is self-issued if the DNs that appear in the subject and issuer
   * fields are identical and are not empty. Note that the last certificate
   * in a certification path is not an intermediate certificate, and is not
   * included in this limit. Usually the last certificate is an end entity
   * certificate, but it can be a CA certificate. A PKIX
   * {@code CertPathBuilder} instance must not build
   * paths longer than the length specified.
   *
   * <p> A value of 0 implies that the path can only contain
   * a single certificate. A value of -1 implies that the
   * path length is unconstrained (i.e. there is no maximum).
   * The default maximum path length, if not specified, is 5.
   * Setting a value less than -1 will cause an exception to be thrown.
   *
   * <p> If any of the CA certificates contain the
   * {@code BasicConstraintsExtension}, the value of the
   * {@code pathLenConstraint} field of the extension overrides
   * the maximum path length parameter whenever the result is a
   * certification path of smaller length.
   *
   * @param maxPathLength the maximum number of non-self-issued intermediate certificates that may
   * exist in a certification path
   * @throws InvalidParameterException if {@code maxPathLength} is set to a value less than -1
   * @see #getMaxPathLength
   */
  public void setMaxPathLength(int maxPathLength) {
    if (maxPathLength < -1) {
      throw new InvalidParameterException("the maximum path "
          + "length parameter can not be less than -1");
    }
    this.maxPathLength = maxPathLength;
  }

  /**
   * Returns the value of the maximum number of intermediate non-self-issued
   * certificates that may exist in a certification path. See
   * the {@link #setMaxPathLength} method for more details.
   *
   * @return the maximum number of non-self-issued intermediate certificates that may exist in a
   * certification path, or -1 if there is no limit
   * @see #setMaxPathLength
   */
  public int getMaxPathLength() {
    return maxPathLength;
  }

  /**
   * Returns a formatted string describing the parameters.
   *
   * @return a formatted string describing the parameters
   */
  public String toString() {
    StringBuffer sb = new StringBuffer();
    sb.append("[\n");
    sb.append(super.toString());
    sb.append("  Maximum Path Length: " + maxPathLength + "\n");
    sb.append("]\n");
    return sb.toString();
  }
}
